I've come to update - we figured out what it is finally! It's our dogs doggy door. See, we never heard it previously as DS's door is always closed, so the sound of it doesnt come through on the monitor.However, last week we got a sparky out to install an electrical socket to plug the new baby monitor into for our new bubs - and kept the nursery door open each night (which is right next to DS's room) So THAT"S why we could hear it so loudly now, and thats why it happens at around the same time each night/morning, and why its always around four bangs before stopping.

First Apple and Facebook announced they would pay $20,000 towards the cost of their female employees freezing their eggs, now IBM in the US has come up with an innovative new policy aimed at retaining female employees.